1. Field of the Invention
This invention relates to a driving control system and monitoring device for the fan filter unit in a semiconductor clean room. More particularly, it relates to a monitoring device that effectively indicates and signals the normal or abnormal operating state of the driving control system for the fan unit.
2. Description of the Related Art
It is known that the production quality and yield of semiconductor devices are greatly affected by the ambient conditions under which they are produced. Accordingly, the semiconductor device manufacturing process is performed in highly-purified clean rooms in which an air stream is continually introduced into the clean room to discharge particles and other impurities. Preferably, the introduced air would flow downward within the clean room, and swirling or parallel air streams should be prevented as best possible.
FIG. 1 is a simplified schematic diagram of a clean room in which the manufacturing equipment is installed along a production line 1. A plurality of fan filter units 3 are provided in the ceiling of the clean room, and a grating 4 is installed on the bottom of the clean room. As shown in FIG. 1, the air introduced into the clean room is filtered through the fan filter unit 3 and flows downward through the clean room and into the grating 4 below. This downward flowing air stream removes the impurities from the production line 1 through the grating 4. Cleanliness in the clean room is maintained, and the recirculated air from the grating 4 is filtered in the fan filter unit 3 to begin another cycle.
FIG. 2 is an enlarged cross-sectional view of the conventional fan filter unit 3 that includes a fan 11, a driving motor 12, which is controlled by its own local control unit 14 with a micro processor provided therein, and a filter 13 for removing impurities mixed with the recirculated air from the clean room. Since the fan filter unit 3 is crucial for maintaining the cleanness of the clean room, the operating state of each of the components of the fan filter units is monitored and controlled by a main computer connected to the components via a computer network.
FIG. 3 is a block diagram illustrating the conventional driving control system of the fan filter unit, wherein a plurality of fan filter units (FFU) 3 are divided into groups depending on their locations or installation lines, and a corresponding plurality of multi-control units (MCU) 15 controls each respective group of FFU's. The multi-control units 15 are integrated into a single host control unit (HCU) 17 through a plurality of relay control units (RCU) 16 corresponding to each group of FFUs. A monitor 18 connected to the host control unit 17 monitors the operating state of all of the fan filter units 3.
The driving control monitoring system of the fan filter unit as mentioned above senses the abnormal operating state of the fan filter unit 3 by the current or voltage flowing through the network connecting each fan filter unit 3 and its local control unit (LCU) 14. However, in some cases, even when the fan filter unit 3 is operating abnormally, the current may continue to flow to the fan filter unit 3. Therefore, the host control unit 17 does not detect the abnormal state of the fan filter unit 3.
The conventional driving control system monitoring function for the fan filter unit 3 thus suffers some drawbacks in that it is not capable of precisely monitoring its operating state, nor can it detect the source for the processing defects.
When the fan filter unit 3 stops operating, the downward air stream is not generated such that the clean room cannot maintain its high standard of cleanness, whereby the production yield decreases due to the contamination of the processing line.